linux-hardening - Re: [PATCH] drm/modes: refactor deprecated strncpy

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Date:   Thu, 14 Sep 2023 21:30:43 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Justin Stitt <justinstitt@...gle.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org, Xu Panda <xu.panda@....com.cn>
Subject: Re: [PATCH] drm/modes: refactor deprecated strncpy

On Thu, Sep 14, 2023 at 06:08:44PM +0000, Justin Stitt wrote:
> `strncpy` is deprecated for use on NUL-terminated destination strings [1].
> 
> We should prefer more robust and less ambiguous string interfaces.
> 
> A suitable replacement is `strscpy` [2] due to the fact that it guarantees
> NUL-termination on the destination buffer and doesn't incur the
> performance loss of unnecessarily NUL-padding.

How did you decide it didn't need %NUL padding?

I suspect it should have it, as I see what looks like full struct copies
happening in places:

        struct drm_mode_modeinfo umode;

	...
                struct drm_property_blob *blob;

                drm_mode_convert_to_umode(&umode, mode);
                blob = drm_property_create_blob(crtc->dev,
                                                sizeof(umode), &umode);

Can you send a v2 using strscpy_pad() instead?

Thanks!

-Kees

-- 
Kees Cook